The invention relates to a lamp ignition circuit having a disabling function which operates with a low-wattage discharge semi-resonant ballast and lamp circuit. Further, the invention relates to a lamp ignition circuit, the disabling function of which does not require the lamp operating voltage to be considerably higher than the ballast open-circuit voltage during lamp run conditions.
A low-wattage discharge lamp circuit which provides lamp-driven voltage transformation and ballasting is described in U.S. Pat. No. 5,825,139 (commonly assigned to Hubbell Incorporated). The lamp circuit described therein uses the discharge breakdown mechanism of the lamp itself at least once each half-cycle to excite a series-connected inductance and capacitance into ringing up to an instantaneous and root mean square (RMS) open circuit voltage (OCV) of approximately twice the input line voltage to drive the discharge lamp. This is in contrast with a conventional gas discharge lamp circuit which supplies higher voltage to the lamp to maintain operation. For example, a conventional gas discharge lamp circuit is typically provided with a semiconductor switching device to augment the source voltage to provide the required lamp ignition voltage.
The measured lamp operating voltage of the lamp circuit described in U.S. Pat. No. 5,825,139 is higher than the line voltage because the lamp itself facilitates its own driving voltage. The lamp circuit is advantageous because it does not require such switching circuits as the aforementioned semiconductor switching device and therefore requires fewer components. Instead, switching operations intrinsic to the lamp shock-excite the inductance and the capacitance into an energy exchange and transfer during each half-cycle at a higher frequency than the frequency of the AC source connected to the lamp circuit. The circuit values for the inductance and capacitance are chosen to allow this semi-resonant operation. In other words, these circuit reactors are different from self-resonant reactors because they are resonant when the switching lamp excites them and therefore are capable of being shocked by the switching action of the lamp. Accordingly, the lamp circuit described in U.S. Pat. No. 5,825,139 is hereinafter referred to as a semi-resonant ballast and lamp circuit.
A lamp starting circuit or ignitor is normally present in a lamp circuit and is typcially switched out of operation, or its influence on the lamp circuit is minimized, by the lamp entering a normal operating mode. Conventional ignitors do not function properly with the semi-resonant ballast and lamp circuit described in U.S. Pat. No. 5,825,139 because they depend upon the lamp operating voltage being considerably lower than the ballast OCV. A need therefore exists for an ignition circuit which can ignite a lamp in a semi-resonant ballast using substantially the line voltage. A need also exists for an ignition circuit which does not require an operational distinction such as the significant difference between the instantaneous OCV and the lamp operating voltage used to provide or withhold ignition pulses in conventional ignitor circuits.
In accordance with the present invention, a lamp ignition circuit is provided which can start and maintain operation of a gas discharge lamp using only line voltage as the activating electromotive force.
In accordance with an aspect of the present invention, a lamp ignition circuit for a semi-resonant ballast and lamp circuit is provided which does not require an operational distinction such as a significant difference between the instantaneous OCV and the lamp operating voltage to provide or withhold ignition pulses as do conventional ignitor circuits.
In accordance with another aspect of the present invention, a lamp ignition circuit is provided which has a disabling function triggered by an increase in voltage across the ignition circuit following operation of the lamp.
A discharge lamp circuit comprises: (1) a discharge lamp operable from an alternating current power source; (2) an inductor; (3) a first capacitor, the inductor, the lamp and the capacitor being connected in series; and (4) an ignitor circuit connected at one end thereof to a first node between the inductor and the lamp and connected at the other end thereof to a second node between the capacitor and the power source. Switching operations intrinsic to the lamp shock-excite the inductor and the capacitor into semi-resonant operation corresponding to an energy exchange and transfer during each half-cycle of the alternating current source to drive the lamp to start and maintain operation of the lamp using line voltage. The ignitor circuit has a disabling function following ignition of the lamp which is operable when the operating voltage of the lamp is approximately the line voltage of the power source.
In accordance with another embodiment of the present invention, an ignitor circuit for a semi-resonant ballast and lamp circuit is provided. The semi-resonant ballast and lamp circuit is operable to use switching operations intrinsic to a discharge lamp to shock-excite a series-connected inductor and capacitor into an energy exchange and transfer during each half-cycle of an alternating current source providing power to the semi-resonant ballast and lamp circuit to start and maintain operation of the lamp using line voltage. The ignitor circuit comprises: (1) a second capacitor; (2) a capacitor charging circuit for charging the second capacitor with an offset voltage; and (3) a pulse generator circuit for generating pulses via discharging of the second capacitor to ignite the lamp when combined with the offset voltage and line voltage from the power source. The pulse generator circuit is connected at one end thereof to a first terminal of the second capacitor. The second capacitor is connected at a second terminal thereof to a first node between the inductor and a first terminal of the lamp. The pulse generator circuit is connected at another end thereof at a second node between the capacitor and the power source. The pulse generating circuit is rendered ineffective for igniting the lamp when voltage across the first node and the second node increases during operation of the lamp. A disabling circuit is provided for the ignitor circuit which is triggered by a voltage corresponding to the root mean square voltage of the power source.
In accordance with yet another embodiment of the present invention, an ignitor circuit for a semi-resonant ballast and lamp circuit comprises: (1) a resistor and a second capacitor connected in a series circuit and across the lamp; (2) a transformer having a primary winding and a secondary winding; (3) a breakover device; and (4) third capacitor connected at one terminal thereof to respective first terminals of the primary winding and the secondary winding and at the other terminal thereof to a return path of the lamp to the power source, the breakover device having a terminal connected to the second terminal of the primary winding and another terminal connected to the series circuit, the second terminal of the secondary winding being connected to the supply side of the lamp. The second capacitor charges through the resistor until a breakover voltage corresponding to the breakover device is reached. The second capacitor discharges through the primary winding to allow the transformer to generate a pulse for igniting the lamp using substantially the line voltage.